The commuter train that crashed Sunday in the Bronx shouldn't have derailed. The four people who died should still be alive. And they would be, if only New York's Metropolitan Transportation Authority had deployed safety technology already used elsewhere and pushed by rail safety watchdogs for 40 years.

Instead, a dazed engineer barreled into a 30 mph curve at 82 miles per hour. No alarm sounded to shake him out of his stupor. No automatic brakes kicked in. Disaster was guaranteed.

All so unnecessary — and so unwise. Five years ago, in the wake of a fatal train accident in California, Congress mandated that all railroads install an automated braking system that could have prevented the crash. The deadline is 2015, but many railroads — wary of the cost — have failed to comply and are pushing for delay. It's fair to wonder what the MTA thinks of that strategy today.

The braking system is designed for incidents just like Sunday's, in which a union official said the engineer had a "momentary nod" at the controls. The National Transportation Safety Board has urged its use for decades.

Back then, the technology didn't exist. Today, digital communications combined with GPS can monitor train locations and speeds, talk to trains and automatically take charge when a train needs to be slowed. About a third of train accidents from 2000 to 2009 were caused by human error, including cases when an engineer fell asleep or became distracted.

It took the horrific 2008 collision in California to finally get Congress' attention. A Metrolink passenger train operator was texting, ran through a stop signal and collided with a freight train. The 25 deaths and 135 injuries pushed lawmakers to mandate that "positive train control" technology be installed on trains that carry passengers or hazardous materials by the end of 2015.

The likelihood that deadline will be met? Close to zero.

Not long after the law's passage, railroads started battling for an extension. Now they want until 2018.

The safety program is undoubtedly complex and costly. But there's one problem with the industry's insistence that the deadline couldn't be met: Some railroads will meet it.

Amtrak has a form of positive train control in operation between Boston and New Haven and in some spots farther south along the Northeast Corridor. Metrolink says its system will be up and running by the end of next year. BNSF, a freight operator, expects to meet the deadline, too.

If they can do it, why can't others?

Some of the obstacles sound real. Commuter systems are often strapped for money. Congress has made available only one-fifth of what was supposed to be a $250 million fund to help with improvements.

Even so, extending the deadline is no solution. It takes the pressure off the delinquents and is unfair to the railroads that have complied.

Accidents happen. But this one was preventable. So is the next one, but only if the railroads act.

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